--- title: "Set up Python for use with Nexus" canonical: "https://help.vicon.com/space/Nexus220/897714887/Set%20up%20Python%20for%20use%20with%20Nexus" format: markdown --- The Nexus API is supplied as a Python package called *viconnexusapi* and is automatically installed with Nexus. The build of Python installed within Nexus is Python 3. You can run the Python SDK for Nexus in a Python 3 environment as well as in a Python 2 environment. For more information, see: > Macro (toc) > Macro (scroll-pagebreak) ## Configure Python for scripting with Nexus **To set up Python to work with Nexus:** 1. Go to Windows Search > Macro (inline-media-image) and start to type `Python`. 2. Click the required Python. 3. To automatically configure Python for scripting with Nexus, at the command prompt, enter one of the following: ##### UsingViconNexusAPI.py ```python from viconnexusapi import ViconNexus vicon = ViconNexus.ViconNexus() ``` ##### UsingViconNexusAPI2.py ```python import viconnexusapi vicon = viconnexusapi.ViconNexus.ViconNexus() ``` The Python installed with Nexus contains the API version shipped with that version. However, if you install the package into another Python distribution, you are responsible for installing the appropriate version. For information on how to access the help provided on the relevant Python commands, see [Python commands for use with Nexus](https://vicon-help.atlassian.net/wiki/spaces/Nexus220/pages/897714912). For more information about how to use Python, see the [Python Getting Started](https://www.python.org/about/gettingstarted/) page. > ⚠️ **Important** > ⚠️ If you disconnect your Ethernet cable and turn off wifi, when you enter a Python command, the following error may be displayed: > ⚠️ `Host Application is not connected, unable to retrieve command list` > ⚠️ This is because Python connects to Nexus over TCP/IP and if you are working entirely offline, Python and Nexus cannot connect. > ⚠️ To solve this issue, install the Microsoft Loopback Adapter. For instructions, see [Install the Microsoft loopback adapter](#InstallLBAdapter). > Macro (scroll-pagebreak) > Macro (anchor) ## Run a Python script from within Nexus In the **Communications** pane, the **Python** tab enables you to set the path to your Python installation and run a script without having to include it in a pipeline operation. > ![PythonTabAdvanced.png](media://6a69710b-0aca-469a-9b14-c8ebafb34a31) **To run a Python script:** 1. On the Python tab, ensure the **Advanced** properties are displayed. 2. In the **Python script file** field, enter or browse to the full path and filename of the Python script you want to run. 3. In the **Script arguments** field, enter any arguments needed by the Python script you specified. 4. In the **Python command** field, select the required Python (for an explanation of the options, see [Launch the required Python](#LaunchRequiredPython)). The default is *python.exe*. 5. If the Python installation you want to use is not in the PATH, in field, in the **Environment activation** field, enter or browse to the full path name of executable file (usually a .*bat* file) that will run in the command shell to configure your Python environment before running the Python script that you specified in the **Python script file** field. The executable should run the commands needed to activate the virtual environment, which could include changing directories, configuring PATH, etc. By default, the **Environment activation** file is the supplied *NexusLocalPython.bat* file. This sets the PATH environment to point to the Python installation provided by Nexus. 6. If you want to launch a Python shell, using the selected Python, click **Python shell**. 7. To run the specified script, click **Run Script**. To create a new pipeline that contains all the above properties with the values you specified, click **Create Pipeline**. Note that the settings in the **Python Script Interface** persist between runs, and the settings for **Python command** and **Environment activation** are used as the initial values when you create a **Run Python Operation** pipeline operation. If you change the parameters for a specific operation in a pipeline, they do not affect the persisted values of the parameters and they do not alter the values of the settings on the panel. ## Install the Nexus API into other Python distributions The build of Python (Python 3) installed within Nexus automatically installs the *viconnexusapi* package as part of Nexus. A script is also available with the installer, which installs the package into the system Python distribution. You can also directly install the package into any other Python distributions that you have installed. ##### Installing_viconnexusapi ```powershell cd "C:\Program Files\Vicon\Nexus2.14\SDK\Win64\Python" # install the api into the system python ./install_vicon_nexus_api.bat # install the api into a specific python distribution -m pip install ./viconnexusapi ``` The advanced modeling scripts are provided as a package called *viconnexusutils *and are available in the same way as *viconnexusapi*, except that these scripts are not automatically installed. This is because they have additional dependencies that cannot be guaranteed to be present and must be downloaded by *pip*. > Macro (scroll-pagebreak) > Macro (anchor) ## Launch the required Python The shell launched by the python operation is either the Python distribution shipped with Nexus or your default Python (as determined by the PATH variable). If the Python distribution shipped with Nexus is launched, the API package is automatically available for import, and additional scripts are not required. If you choose to use a Python that is different from the installed Nexus distribution, you can use an advanced option to select the command used to launch Python. The options for this are **python.exe** or **py.exe**: - If you have only a Python 2 **or** a Python 3 installation in the path, **python.exe** launches that version of Python. - If you have both versions and the *pylauncher* utility, **py.exe** launches either Python 2 or Python 3, depending on a shebang comment at the start of the launched script. ### CGM2 Python version CGM2 launches using the version of Python 3 installed with Nexus. Note that: - To ensure pyCGM2 continues to operate correctly, do not modify the Python installation that is installed with Nexus. - Do not use versions of pyCGM2 other than that supplied by Vicon. Using other versions of pyCGM2 may cause Nexus operations to fail. (If you want to use a different version of pyCGM2 for comparison purposes, create pipelines with the **Environment activation** file set appropriately in the pipeline operation(s).) - If you customize your Python environment, note that it is assumed that the *Scripts* folder that contains the pyCGM2 scripts is the current folder after the **Environment activation** file has finished running. > Macro (anchor) ## Install the Microsoft loopback adapter **To install the Microsoft loopback adapter on Windows 11:** 1. Right-click the Windows **Start** menu icon and select **Device Manager** (or use your preferred method of opening the Device Manager). 2. In the **Device Manager**, select any item in the **Common hardware types** list. 3. From the **Action** menu, select **Add legacy hardware**. 4. On the welcome screen, click **Next**. 5. In the **Add Hardware** dialog, select **Install the hardware that I manually select from a list** and then click **Next**. 6. In the next dialog, scroll down the **Common hardware types** list, select **Network adapters** and then click **Next**. 7. From the **Manufacturer** list, select **Microsoft**, and then select **Microsoft KM-TEST Loopback Adapter **card model and click **Next**. 8. In the next screen, click **Next**. 9. Click **Finish**.